新手求助~（关于初级的神经网络问题）

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各位大虾，我在网上看到的教程里的一个程序段，本来想要试试看的：
* N" Y( M8 p5 ]' \0 I  fnet=newff([-1 2; 0 5],[3,1],{'tansig','purelin'},'traingd');

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6 s- J! e0 \  B/ |0 Dnet.trainParam.show = 50;
' {- d" Z! x9 @( Znet.trainParam.lr = 0.05;
net.trainParam.epochs = 300;
, f& ?2 k7 {, Z) Dnet.trainParam.goal = 1e-5;
p = [-1 -1 2 2;0 5 0 5];
+ m9 s3 I, E4 l$ |& X8 k# ?# Y* Xt = [-1 -1 1 1];

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net=train(net,p,t);
TRAINGD, Epoch 0/300, MSE 1.59423/1e-05, Gradient 2.76799/1e-10


% g/ h4 A; K, ?4 ETRAINGD, Epoch 50/300, MSE 0.00236382/1e-05, Gradient 0.0495292/1e-10
- X) l7 d4 ]: i6 d& `) |" A4 |TRAINGD, Epoch 100/300, MSE 0.000435947/1e-05, Gradient 0.0161202/1e-10
. V6 w0 n! ~% h# M4 z/ qTRAINGD, Epoch 150/300, MSE 8.68462e-05/1e-05, Gradient 0.00769588/1e-10
TRAINGD, Epoch 200/300, MSE 1.45042e-05/1e-05, Gradient 0.00325667/1e-10
TRAINGD, Epoch 211/300, MSE 9.64816e-06/1e-05, Gradient 0.00266775/1e-10
TRAINGD, Performance goal met.
a = sim(net,p)
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% v7 N+ h. w$ Y8 [0 B4 v
plot(p,t,p,a,'o')


8 [7 U2 a5 j8 D0 i1 R8 `但是为什么老是报错：
??? Input argument "net" is undefined.